The use of prepared mixes and batters has greatly simplified the task of preparing baked goods, in particular, cakes which contain flour, sugar, shortening, leavening agents, and other minor ingredients. To prepare cakes for use, the liquid ingredients such as oil, water, milk, and or eggs are added to the mix and stirred to form a homogeneous batter. This batter is subsequently baked to produce a final layer. Alternatively, the dry and liquid components can be assembled to make a batter prior to delivery to the consumer to further simplify the task of preparing baked goods. The use of such mixes and batters avoids the problems of assembling the various ingredients, measuring the desired quantities, and mixing them in the specified proportions.
The use of microwave ovens for baking has greatly simplified the baking process by reducing the time required for baking. Additionally, the baked goods can often be baked in a container that can be used for serving the product.
In a conventional oven, the process of cooking to the center of the food mass by conduction requires a temperature gradient, in which the surface temperatures are usually much higher than the final cooked temperature of the food. For example, a gas-fired oven may be maintained at 300.degree.-400.degree. F. to produce a baked cake layer. Under these conditions, browning of the surface of the cake layer is readily obtained. In microwave cooking, on the other hand, the ambient temperature in the cooking space is approximately room temperature. Any rise in temperature in this space is due to heat loss from the food to its environment. In a microwave oven, alternating electromagnetic fields are generated by a magnetron oscillating at a frequency of approximately 2450 megahertz. Some of the incident energy of electromagnetic waves, which are called microwaves at this frequency, is immediately absorbed within the food mass. The resulting increase in thermal energy (heat) in the food depends on an interaction between the microwave energy and the materials or components of which the food is composed. The dielectric properties (e', the relative dielectric constant and e", the relative dielectric loss factor) described how these components interact with the microwave field. This interaction occurs throughout the food mass, instantly produces heat, and results in rapid cooking.
Normally, food is cooked in utensils which are not very absorptive of microwave energy. Economy of energy is inherent in the microwave method compared with conventional ovens, in which the temperature of the environment is raised, in order to heat and cook through the mass of food by conduction and/or convection. However, this economy of energy has important consequences which affect the acceptance of foods cooked by the microwave method. The food habits of consumers heretofore have required that the food surface have certain familiar characteristics. The normal charred appearance of steak, the deep brown color of roast beef, and the golden brown color of pie crust are notable examples.
It has thus been found that foods cooked by microwaves may have somewhat different characteristics from foods cooked in a conventional oven, and it may be possible to take advantage of these differences in preparing foods in a microwave oven.
When a cake system, for example, a slab, toroid, or other shape, is placed in a microwave field, certain regions of the product heat more than others. In a standard layer cake, largely, this is due to a geometry effect whereby the edges are irradiated from three sides and the center receives energy primarily from only two sides. Another reason for the uneven delivery of microwave energy to products includes the presence of "hot spots" that are specific to individual microwave ovens. These are caused by microwave radiation interference patterns occurring due to the geometry of the oven cavity. Still another cause of uneven delivery of energy within a cake system, whether of one or more layers, is due to the variation in energy absorption with the thickness and dielectric characteristics of each layer. This has been described more fully in Ser. No. 903,007 and the CIP Ser. No. 085,125, filed Aug. 13, 1987, Atwell et al., for Microwave Food Product and Method, which applications are incorporated herein by reference.
The uneven heating resulting from this uneven energy distribution causes convection currents to occur in many fluid systems such as cake batters. Generally, in a standard size layer cake system, there is an upward flow at the edges and a downward flow in the center during microwave preparation. Random flow of batter due to microwave interference patterns or uneven delivery of energy within a layer can also occur. This turbulent flow can cause disruption of layer integrity in a multilayer microwave cake system. Integrity is defined as having distinct boundaries between the layers and having layer thickness which boundaries and thickness remain substantially unchanged during the cooking process.
Microwave cake viscosity has been evaluated with microwave preparation time, and it has been determined that some portions of the batter set fairly early in the baking process. Lumps or discrete regions of set batter are apparent around the edges of the microwave cake batter after approximately 1-2 minutes at high power in a 700 watt microwave oven. A clear relationship between viscosity and temperatures has not been identified for temperatures above 50.degree. C. due to this setting phenomenon and the corresponding high viscosities. It can be concluded from these observations that the turbulent flow contributing to a loss of layer integrity in a multicomponent batter system is confined to pre-setting viscosities and is probably largely occurring in the initial stages of the baking process.
White Wings markets a microwave cake/glaze mix in Australia. However, in this product the glaze or topping is very fluid after baking and removal from the pan, does not remain in position, and does not remain as a separate, integral layer after baking. The package provides no separate formulations for the cake or glaze components.